Mechanism of reflex regulation of the gastroduodenal function by acupuncture

Abstract

Many clinical studies focus on the effects of acupuncture on digestive disorders. However, few studies describe the mechanism by which these effects are produced. We present some recent experimental work on the mechanism of acupuncture for reflex regulation of gastroduodenal function in anesthetized rats. In anesthetized rats, it has been proven that acupuncture to the abdomen excites sympathetic nerves via spinal reflexes causing inhibition of motilities while acupuncture of limbs excites vagus nerves via supraspinal reflexes causing an increase in the motilities. It has also been shown that in order to inhibit gastric motilities, acupuncture stimulation of the abdomen must be strong enough to excite group VI fibers of the afferent intercostal nerves. To increase gastric motilities, acupuncture stimulation to hind limbs must be strong enough to excite the high-threshold group III fibers of tibial nerves. It has also been shown that the neural mechanism of duodenal motility stimulation by acupuncture involves the same body regions and intensity of stimulation as that of gastric motilities. Theories regarding the underlying mechanism have proposed somato-autonomic reflexes and responses via endogenous opioids, etc., but without definitive conclusions.

Keywords: duodenal motility; gastric motility; gastric-acid secretion; rat; somato-autonomic reflex.

Figure 1.

Changes in gastric motility caused by acupuncture. (A) A frame format showing gastric motilities caused by acupuncture in each dermatome. Open or closed circles showed regions of the excitatory or inhibitory gastric motilities. Circle size indicates the levels of each response shown in the figures. (B, C) Effects of acupuncture stimulation of the abdomen (B) and hind paw (C). Gastric motilities (upper traces), efferent gastric sympathetic nerve activity (middle trace) and efferent vagus nerve activity (lowest trace) after acupuncture. Activity of each nerve was continuously measured and level of acupuncture stimulation/minute is expressed with horizontal bars. (D) Pathway for reflex regulation of the gastric motilities of anesthetized rats. [Quoted from Sato with modification (10)].

Figure 2.

Changes in gastric motilities with electro-acupuncture. Measurements of gastric motilities were the same as in Fig. 1. (A) Inhibitory changes of gastric motilities from abdominal stimulation with electro-acupuncture. (B) Excitatory changes of gastric motilities by stimulation of hind limb with electro-acupuncture. (C) Comparison between the intensity of abdominal stimulation with electro-acupuncture and the rates of gastric motility changes. As shown with arrows, Ta and Tc indicate the average intensity of threshold of group A and B fibers in the afferent intercostal nerve activity. Significant inhibitory changes were induced by intense stimulation above the threshold of group C fibers. (D) Comparison between the intensity of hind paw stimulation with electro-acupuncture and the rates of gastric motility change. As shown with arrows, Ta and Tc indicate the average intensity of threshold of group A and B fibers of the tibial nerves, respectively. Significant increase was induced by intense stimulation of group A fibers with high thresholds. Changes in average intragastric pressure are expressed as a percentage before stimulation. *P < 0.05 (**P < 0.01) indicates significant differences in reference to prestimulatory values with paired t-test analysis. [Cited from Yamaguchi with modification (14)].

Figure 3.

Changes in duodenal motilities stimulated by electric acupuncture. (A) Intensity of electro-acupuncture to the abdomen and hind paw and the rate of changes in duodenal motilities. (A-1) The threshold of afferent intercostal nerve activity innervating the stimulated abdominal region, and the inhibitory change rates of duodenal motilities. T_I–IV arrows indicate the threshold of afferent intercostal nerve activity of each nerve. A significant inhibitory response appeared with stimulation above the intensity that excited group IV fibers. (A-2) The threshold of afferent tibial nerve activity innervating the stimulated hind paw region, and the inhibitory change rates of duodenal motilities. T_II–IV arrows indicate the threshold of afferent tibial nerve activity for each nerve. A significant inhibitory response appeared with stimulation above the intensity threshold of group III or IV fibers with high thresholds. Particulars of the statistical analysis are the same as Fig. 2. (B) Effects of the vagotomy. (B-1) No inhibitory response of the duodenal motilities, (B-2) disappearance of excitatory response. (C) Effects of the splanchnic nerve section. (C-1) Disappearance of inhibitory response of duodenal motilities, (C-2): no effect on excitatory response. (D) Effects of the spinal cord section. (D-1) No effect on inhibitory response of duodenal motilities, (D-2) disappearance of excitatory response (Cited from Noguchi with modification [15]).

Figure 4.

Changes in gastric acid secretion with electro-acupuncture. (A) Effects of severing the splanchnic nerve and vagus nerve on excitatory response of gastric acid secretion with electro-acupuncture of the hind paw of the anesthetized rats at acupuncture point S-36 Excitatory response of gastric acid secretion with electro-acupuncture disappeared after vagotomy (open squares) and ischiadic nerve section (closed squares), while that after the splanchnic nerve section did not disappear. Horizontal lines (EAS) indicate the period of acupuncture stimulation. [Cited from Noguchi with modification (20)]. (B) Effects of electro-acupuncture stimulation on gastric acid secretion after amino acid intake in conscious dogs. No AP: control without stimulation, EAP: electro-acupuncture, EAP + Naloxone: acupuncture stimulation + Naloxone (40 g/kg⁻¹/h⁻¹), AAMeal: amino acid intake (given in all experiments). Horizontal lines (EAS) indicate the period of acupuncture stimulation. Electro-acupuncture inhibited gastric acid secretion after amino acid intake (open squares). However, this suppressive response was inhibited by naloxone administration (closed squares). [Cited from Jin et al. with modification (18)].